Interlayer insulating films have been used in the production of image displays (e.g., liquid-crystal displays) or semiconductor devices. In general, interlayer insulating films have a pattern formed by etching, via a photoresist, a film formed by deposition from a vapor phase or by application. For forming a fine pattern, vapor phase etching has usually been used. However, the vapor phase etching presented the problems of high apparatus cost and slow performance.
Thus, photosensitive materials for interlayer insulating films have been developed for the purpose of cost reduction. Particularly, in liquid-crystal displays, interlayer insulating films used for insulation between pixel electrodes and gate/drain wiring and for device flattening require forming a contact hole therein. Therefore, photosensitive materials for interlayer insulating films have been demanded, which have positive-type photosensitive properties. The interlayer insulating films in liquid-crystal displays are further demanded to have transparency. Additionally, when a residual patterned film is used as an interlayer insulating film, the film is demanded to have small permittivity.
In response to these demands, methods disclosed in, for example, Patent Documents 1 and 2, have been proposed. Patent Document 1 discloses a method for forming an interlayer insulating film, comprising the steps of: forming an applied coating of a photosensitive polysilazane composition comprising polysilazane and a photoacid generator; irradiating the applied film with light according to a pattern; and removing, by dissolution, the irradiated portion in the applied film. Additionally, Patent Document 2 discloses an interlayer insulating film which is formed from a composition comprising: a siloxane resin; and a compound that generates an acid or base upon exposure to radiation.
Here, the terms “radiation sensitivity” and “photosensitivity” are defined. According to “Non-Patent Document 1”, the term “radiation” is defined as “every electromagnetic wave and particle beam” in the broad sense and encompasses light. Thus, although both the terms “radiation sensitivity” and “photosensitivity” are described in the present specification, the former is used in the broader sense. When light is used as a source, these terms are synonymous with each other.    [Patent Document 1] Japanese Patent Laid-Open No. 2000-181069    [Patent Document 2] Japanese Patent Laid-Open No. 2004-107562    [Non-Patent Document 1] Dictionary of Physics and Chemistry (Rikagaku Jiten in Japanese) 3rd ed., Iwanami Shoten, Publishers, p. 1262